Carriers, equipment manufacturers, and enterprises are embracing IP telephony and other IP-based media communications with increasing regularity. These IP-based communication networks present a difficulty in that their openness makes them vulnerable to security issues. As a result, most IP networks contain firewalls at various points.
Firewalls present a particular difficulty for peer-to-peer or multimedia communications, which are typically transmitted using UDP (User Datagram Protocol) packets. This poses difficulties for applications such as IP telephony, sometimes called voice-over-IP (VoIP), and for other peer-to-peer or multimedia applications, such as IP fax, video phones, interactive gaming, and other UDP-based media. Typically firewalls only permit incoming communications that meet certain firewall rules. Accordingly, UDP packets may be blocked by a firewall.
As more carriers begin to offer interactive gaming, VoIP and other IP telephony services, and as more enterprises offer VoIP to remote employees connecting to an enterprise network through a VPN (Virtual Private Network) connection, there needs to be a solution to the problem of traversing a firewall without eliminating the firewall altogether.
One solution that has been attempted in the past is the establishment of application level gateways (ALGs) within the firewall itself. The limitations of this solution include the fact that ALGs are protocol-specific, which presents a problem since the ALG must inspect, parse and understand the various protocols that may be used. Any changes to the protocol may render the ALG ineffective. The ALG solution also imposes a significant cost on firewall resources in terms of memory and processing. It would be preferable to have a protocol independent solution for firewall traversal